Starter code for the Units app for teaching Testing in Android

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

  <androidx.appcompat.widget.SwitchCompat
      android:id="@+id/switch_c_f"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_marginStart="8dp"
      android:minWidth="48dp"
      android:minHeight="48dp"
      app:layout_constraintBottom_toBottomOf="@+id/txt_c2f"
      app:layout_constraintEnd_toStartOf="@+id/txt_f2c"
      app:layout_constraintHorizontal_bias="0.5"
      app:layout_constraintStart_toEndOf="@+id/txt_c2f"
      app:layout_constraintTop_toTopOf="@+id/txt_c2f" />

  <TextView
      android:id="@+id/txt_c2f"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="@string/c2f"
      app:layout_constraintBottom_toTopOf="@+id/edit_input"
      app:layout_constraintEnd_toStartOf="@+id/switch_c_f"
      app:layout_constraintHorizontal_bias="0.5"
      app:layout_constraintHorizontal_chainStyle="packed"
      app:layout_constraintStart_toStartOf="parent"
      app:layout_constraintTop_toTopOf="parent"
      app:layout_constraintVertical_chainStyle="packed" />

  <TextView
      android:id="@+id/txt_f2c"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_marginStart="8dp"
      android:layout_marginEnd="8dp"
      android:text="@string/f2c"
      app:layout_constraintBottom_toBottomOf="@+id/switch_c_f"
      app:layout_constraintEnd_toEndOf="parent"
      app:layout_constraintHorizontal_bias="0.5"
      app:layout_constraintStart_toEndOf="@+id/switch_c_f"
      app:layout_constraintTop_toTopOf="@+id/switch_c_f" />

  <EditText
      android:id="@+id/edit_input"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_marginTop="16dp"
      android:autofillHints="Signed Decimal Number"
      android:ems="10"
      android:hint="@string/input_value"
      android:inputType="numberDecimal|numberSigned"
      android:minHeight="48dp"
      android:textAlignment="center"
      app:layout_constraintBottom_toTopOf="@+id/btn_convert"
      app:layout_constraintEnd_toEndOf="parent"
      app:layout_constraintHorizontal_bias="0.5"
      app:layout_constraintStart_toStartOf="parent"
      app:layout_constraintTop_toBottomOf="@+id/txt_c2f"
      tools:ignore="TextContrastCheck" />

  <Button
      android:id="@+id/btn_convert"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="@string/convert"
      app:layout_constraintBottom_toBottomOf="parent"
      app:layout_constraintEnd_toEndOf="parent"
      app:layout_constraintStart_toStartOf="parent"
      app:layout_constraintTop_toBottomOf="@+id/edit_input" />

  <TextView
      android:id="@+id/txt_output"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:textAlignment="center"
      android:textAppearance="@style/TextAppearance.AppCompat.Large"
      app:layout_constraintEnd_toEndOf="parent"
      app:layout_constraintHorizontal_bias="0.5"
      app:layout_constraintStart_toStartOf="parent"
      app:layout_constraintTop_toBottomOf="@+id/btn_convert" />
</androidx.constraintlayout.widget.ConstraintLayout>

strings.xml

<resources>
  <string name="app_name">Units</string>
  <string name="c2f">C2F</string>
  <string name="f2c">F2C</string>
  <string name="convert">Convert</string>
  <string name="input_value">Input Value</string>
</resources>